1. Field of the Invention
The present invention relates to a vibration-type driving apparatus which is a so-called vibration wave motor causing a moving member to come into contact with a vibration member (vibrating member) in a pressurized state so as to perform a frictional driving action.
2. Description of the Related Art
In general, a vibration-type driving apparatus (vibration wave driving apparatus/a vibration wave motor) includes a vibration member that generates a traveling wave and a moving member that comes into contact with the vibration member in a pressurized state, where a driving force is obtained by frictionally driving the vibration member and the moving member using the traveling wave.
The related art of this kind of vibration-type driving apparatus is shown in FIG. 6A (for example, see U.S. Pat. No. 5,164,629).
In FIG. 6A, a vibration member 42 fixed to a housing 41 is formed in an annular shape, and a plurality of protrusions 42c are provided at the upper portion of an elastic body 42b throughout the entire circumference thereof.
Piezoelectric ceramics 42a are affixed to the bottom surface of the elastic body 42b by adhesive, and two alternating-current voltages with a phase difference are applied thereto from a driving circuit (not shown) when driving a motor, whereby a traveling wave is generated.
A moving member 43 includes an annular body portion 43a that is formed of an elastic member, a supporting portion 43b, and a contacting portion 43c that has a friction surface coming into frictional contact with the protrusions 42c of the vibration member 42.
The supporting portion 43b and the contacting portion 43c are both formed so as to have a thickness with a spring property, and are designed to stably come into contact with the vibration member 42.
A pressurizing spring 46 is attached to the top surface of the moving member 43 with a spring receiving member 44 and a rubber plate 45 interposed therebetween. The inner peripheral portion of the pressurizing spring 46 is attached to a disk 47 shrink-fitted to the output shaft 48, thereby transmitting the driving force of the moving member 43 to an output shaft 48.
The spring receiving member 44 includes a vibration damping rubber 44a and an annular weight member 44b. Accordingly, it is possible to prevent unnecessary vibration from being generated in the moving member 43 and prevents noise or reduction of efficiency.
However, as disclosed in the related art, even when unnecessary vibration is prevented by the vibration damping rubber 44a and the weight member 44b, the performance of the vibration-type driving apparatus may be degraded when the apparatus is driven for a long period of time.
Specifically, the contacting portion 43c of the moving member 43 comes into contact with the vibration member 42 as shown in FIG. 6B.
In FIG. 6B, when a traveling oscillating wave is generated in the vibration member 42, the top surface of the protrusion 42c of the vibration member 42 is vibrated in the direction indicated by the arrow of the drawing, and the top surface vibrates the moving member 43 through the contacting portion 43c. At this time, the direction of the excitation force generated from the vibration member 42 and received by the contacting portion 43c of the moving member does not pass through a centroid 43f of the moving member 43. Here, the centroid indicates the center of the figure, and the center of the figure indicates a coordinate point where the total sum of the geometrical moment of the area becomes 0.
For this reason, the excitation force generated from the vibration member 42 serves as a torsional moment with respect to the body portion 43a of the moving member 43. Due to the torsional moment, torsional vibration is generated in the body portion 43a so as to be alternately twisted about the vicinity of the centroid as shown in FIG. 6C.
Since the torsional vibration is generated as forced vibration which is forcedly excited by the driving frequency, noise such as so-called squealing sounds does not occur.
However, when the torsional vibration is superimposed with the traveling wave of the vibration member 42, the vibration amplitude of the composite vibration becomes uneven. For this reason, when the vibration-type driving apparatus is driven for a long period of time, the wear of the contacting portion 43c of the moving member 43 is unevenly promoted in the circumferential direction, which causes uneven wear.
When uneven wear occurs, there is concern in that the vibration member 42 and the moving member 43 may not be maintained to stably come into contact with each other, the performance of the vibration-type driving apparatus may be degraded, or squealing sounds may occur.
The invention is made in view of such circumstances, and it is an object of the invention to provide a vibration-type driving apparatus that suppresses unnecessary vibration generated with the driving of the vibration-type driving apparatus and reduces degradation of the performance even when the apparatus is driven for a long period of time.